"Wow!" wrote one blogger after reading this paper's disclosure of ministers' plans to ramp up the provision of greener energy. And if they were actually put into practice, he or she vowed, "I will dance around the house singing hallelujah!" Which about sums up the astonishment many environmentalists felt about yesterday's announcement. Such ambition from a government already so far behind its renewables targets? From the prime minister who went to Saudi Arabia at the weekend to ask for more oil? From the energy minister who admitted just a few weeks ago to negotiating with the EU to reduce the UK's green commitments? Surely it was too good to be true?

We shall see. But judging by yesterday's statements, the government has at last got serious about the need to move the UK from being an economy ever-more hooked on gas and oil from abroad to one that generates its own, cleaner energy. It was not just the promise of 30 times the amount of offshore wind power, 7m solar water-heating systems, reducing energy demand - all by 2020 - it was also the language used. Gordon Brown forecast "the most dramatic change in energy policy since the advent of nuclear power" while admitting it would be a wrench - and an expensive one at that. The economy will not grow as fast as it otherwise would have done and all these new plants should cost about £100bn, most (if not all) of which will eventually land on household bills. "Green tax to hit gas bills" was how one paper responded to the plans yesterday; Mr Brown had better get used to such headlines.

In the face of such resistance, it would be natural for any politician (let alone one so far behind in the polls) either to back down or find some wiggle room. The key thing, however, is that after having set explicit targets, Mr Brown has locked in his government, and all those that follow. He has given greens plenty of yardsticks to measure him against. Sceptics point out that these are still only targets and that this necessary transition would not have been so costly had it begun years ago. True enough, but this is still progress after a decade of ministerial foot-dragging and review after interminable review. It also leaves David Cameron and the Conservatives much to do if they want to regain the initiative on green politics. Mr Cameron has helped focus attention on climate change; he has yet to outline a strategy. The Tories remain split on onshore wind farms, the most viable of all renewables, which leaves them pinning their hopes on tidal power, and carbon capture and storage - technologies so far off they might as well feature in the Jetsons.

Such a bold programme inevitably raises questions. Two stand out: one technical, the other philosophical. First, to reach the UK's binding target of sourcing 15% renewables within 12 years will require up to three times the rate of environmental building seen in Germany, the big country with the largest green industry. And the UK is joining this race late, bidding for wind turbines and suitable engineers at just the point they are in ferocious demand around the world. Labour can talk all it likes about stripping down the planning system and leaning on regulators and the National Grid to facilitate this "green revolution", but the bottlenecks are even more basic. No wonder Sue Ion from the Royal Academy of Engineering flatly describes the plan as "not achievable".

The scheme also leaves it up to companies to decide whether to invest in renewables. Can the market be relied on to achieve such big and rapid change? A few weeks ago, Shell pulled out of the London Array wind farm - knowing all the flak it would get. The cumbersome system of subsidies is not as effective as other schemes, such as giving a guaranteed price to producers of green energy . As an energy policy, this could be called "market-plus": all the benefits of business competition, with just a few sweeteners. It may not be enough.